65.CHEMICAL BONDING (12)- Covalent Bonding(11)- sp3d Hybridization(6).

In the last few posts we studied about the most common types of hybridization namely –sp3, sp2 and sp hybridization. These are exhibited predominantly by elements in second period of the periodic table(e.g. Carbon, Oxygen, Nitrogen, Beryllium etc).

 

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Elements which show sp3, sp2 and sp hybridization.

 However, the concept of hybridization can be extended to the p- block elements(e.g.- Suphur, Phosphorous, Iodine etc ) as well.The p-block elements have vacant d-orbitals of similar energy (NOT SAME) , as that of valence s and p orbitals . Thus, the electrons from s orbital can be excited to the vacant d- orbitals.Then the s, p and d orbitals mix to form sp3d, sp3d2 or sp3d3  hybrid orbitals.These type of hybridizations are different than the earlier ones as they involve the vacant d-orbitals.

sp3hybridization .

The process of mixing of one s- orbital ,three p- orbitals and one d-orbital in an atom to form five spd hybrid orbitals of equivalent energy is called spd hybridization.

 

EXAMPLE 1 – PHOSPHOROUS PENTACHLORIDE (PCl)

Phosphorous is a p-block element (Group 15, non-metal).It is the central atom in PCl5  and  is sp3d hybridized.

Phosphorous (15) 1s2 2s2 2p6 3s2 3p3 → Ground state. 

One s – electron promoted to d orbital → 1s2 2s2 2p6 3s1 3p3 3d1.

The 3s , three 3p and one 3d orbitals hybridize to form sp3d hybridization. The molecule is then formed with 5 chlorine atoms.

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Phosphorous pentachloride has a trigonal bipyramidal geometry with 90º and 120º bond angles. The angle between the equatorial chorine atoms is 120º and that between the equatorial and axial chorine atoms is 90º as shown in the figure below – 

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Now what happens when a lone pair is involved in sp3hybridization? How does the geometry change? Let’s study that with an example –

EXAMPLE 2 – SULFUR TETRAFLUORIDE (SF4).

Sulphur too is a p-block element as it has it’s valence electrons in the 3p orbital. It has vacant 3d orbitals ,to which an 3s electron can be promoted easily (as the energy difference between 3s, 3p and 3d is not much ) to undergo sp3hybridization.

Sulphur  1s2 2s2 2p6 3s2 3p→ Ground state.

Sulphur 1s2 2s2 2p6 3s1 3p4 3d→ Excited state.

The 3s , three 3p and one 3d orbitals hybridize to form sp3d hybridization. The molecule is then formed with 4 chlorine atoms.

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The lone pair of electron , needs more space and so it pushes the other electrons. This gives the molecule a seesaw shape .

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We continue our discussion about hybridization in our next post.Till then,

Be a perpetual student of life and keep learning …

Good Day !

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